The current location is now posing a trip hazard for my deck stairs in addition to being below the snow clearance height. There are several concerns that I need to consider with the new placement.

NFGC - Code states:
12.9.2 A mechanical draft venting system of other than direct-vent type shall terminate at least 4 feet below, 4 feet horizontally from, or 1 foot above any door, operable window, or gravity air inlet into any building.
12.9.3 The vent terminal of a direct-vent appliance with an input of 10,000 Btu/hr or less shall be located at least 6 inches from any air opening into a building, and such an appliance with an input over 10,000 Btu/hr but not over 50,000 Btu/hr shall be installed with a 9 inch vent termination clearance, and an appliance with an input over 50,000 Btu/hr shall be at least a 12 inches vent termination clearance.

explanation of the code: Subsection 12.9.3 permits the vent terminals of direct vent appliances to be located much closer to air inlets than is provided for with mechanical draft equipment. There is often a mis application of rules for mechanical draft to direct vent equipment. The vent gases from direct vent equipment disperse rapidly upon leaving the vent terminal, even when the terminal is located under an open window.

installation instructions/code also state that the exhaust needs to be 4' to the side of a combustion air inlet to any other appliance. also, 24" vertically to an unventilated sofit

What I cannot determine what my unit is classified as. It's listed as a "power vented gas water heater" but is it a "mechanical draft venting system' or a "direct vent".

I also have two concerns. 1) how far horizontally does this need to from the input for my 95% furnace (the furnace is a dual pipe configuration - intake and exhaust are both piped to the outside) and 2) can this unit exhaust 24" below an openable window. The window is a bump out 24" above the proposed vent termination.

The products of combustion can pose a problem for a direct vented system, so you would not want the WH vent to be too close to the furnace's. Personally, whether it is allowed or not, I would not want those exhausts beneath a window.

The products of combustion can pose a problem for a direct vented system, so you would not want the WH vent to be too close to the furnace's. Personally, whether it is allowed or not, I would not want those exhausts beneath a window.

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Or even under an overhanging cantilevered floor, since that is a notorious location for infiltration leakage into houses. (If you haven't already, air-seal and insulate those joist bays where they cross over the foundation, and the foundation sill too. Use a blower door or large window fans and to both pressurize & depressurize the house while air sealing, tracing the leak points with a smoke pencil to make sure you nail all of 'em.)

Or even under an overhanging cantilevered floor, since that is a notorious location for infiltration leakage into houses. (If you haven't already, air-seal and insulate those joist bays where they cross over the foundation, and the foundation sill too. Use a blower door or large window fans and to both pressurize & depressurize the house while air sealing, tracing the leak points with a smoke pencil to make sure you nail all of 'em.)

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Thanks for the tips but I really just need to know if it is permissible to relocate the vent to his proposed location 4ft to the right of the furnace input/output location. The exhaust for the furnace passed inspection at its current location so I'm assuming the 24" under the window is allowable. (I know, common sense dictates that the window would be closed during the time when the furnace is running but I can't imagine that matters when it comes to code- it's either allowed or it's not) I'm really not going to get into pressurizing the whole house to check for a leak of air.

Given that power vented burners depressurize the house WHILE they are running, simply not bothering to air seal and test the integrity of the air seal at that critical location seems imprudent. The typical measured leakage at foundation sills is well in excess of windows, even LEAKY windows. When a gas burner is operating properly the health risks of leakage at that location are pretty low, but over the lifecycle of the unit virtually all gas burners will misfunction at some point.